1. Field of the Invention
This invention relates to an automatic umbrella, more particularly to an automatically spreading and collapsing umbrella which can be quickly collapsed with the aid of a collapsing tension spring and a resilient wire.
2. Description of the Related Art
Referring to FIG. 1, a conventional automatically spreading and collapsing umbrella is shown to include an elongate handle 10 with an upper end, a lower end and a middle portion therebetween, a ferrule 20 which is fixed on the upper end of the handle 10 for mounting a canopy 60, a tubular runner 30 which is sleeved slidably on the middle portion of the handle 10, a plurality of rib assemblies (only one is shown) which are disposed at an underside of the canopy 60 to support the canopy 60 in a spread-out position and in a collapsed position, and a plurality of stretcher assemblies (only one is shown) which interconnect the rib assemblies and the runner 30 so as to permit stretching and retracting of the rib assemblies in order to disposed the canopy 60 in a selected one of the spread-out position and the collapsed position when the runner 30 is moved along the handle 10. Each rib assembly includes a main rib 41, a top rib 42 and an extending rib 43. Each stretcher assembly includes a stretcher 44 which is pivotally connected to the runner 30 and the main rib 41, and a connecting rod 45 which has one end pivotally connected to the stretcher 44 and the other end formed with a sliding slot 451 (see FIG. 4) for sliding engagement with the top rib 42 by means of a pivot pin 421.
For automatically collapsing the rib assembly, a collapsing tension spring 50 and a resilient wire 46 are disposed between the rib assembly and the stretcher assembly. With reference to FIGS. 2 and 3, the resilient wire 46 is formed with a straight wire portion 461 at one end thereof. The straight wire portion 461 passes transversely through the main rib 41 for engagement with one end of the tension spring 50. The other ends of the resilient wire 46 and the tension spring 50 are respectively connected to an engaging hole 452 (see FIG. 4) in the extending rib 43 and the connecting rod 45. As such, stretching of the rib assemblies will extend the tension spring 50 to store an elastic potential energy for restoring the tension spring 50 to facilitate collapsing of the rib assemblies. At the same time, the resilient wire 46 can actuate the extending rib 43 to retract inwardly toward the top rib 42.
However, the collapsing operation of the rib assemblies of the conventional umbrella is not smooth, and a lateral force is needed to be applied on the rib assemblies. As shown in FIG. 4, when the rib assembly is stretched, the extending lengths of the connecting rod 45 and the tension spring 50 are almost parallel to each other. That is, a collapsing angle (.gamma.) is defined between reference lines (A) and (B). The reference line (A) is defined by the extension from the engaging hole 452 via the pivot pin 421. The reference line (B) is defined by the extension of the tension spring 50. The greater is the collapsing angle (.gamma.), the easier will be the collapsing operation of the rib assemblies. The collapsing angle (.gamma.) is very small in the conventional umbrella, thereby resulting in adverse affect to the collapsing operation of the tension spring 50.